1. Field of the Invention
This invention relates to a method for producing a catalyst. More specifically, it relates to a method for producing a catalyst which comprises controlling the liquid level of the top face of a monolithic carrier by a water-detecting sensor, especially a method for producing an exhaust gas purifying catalyst.
2. Description of Related Art
In the deposition of a catalytically active component on a monolithic carrier, when the expensive active component is deposited also on the lateral face of the carrier, such lateral face so deposited does not treat exhaust gases and it rather brings the disadvantage of heightening the price of produced catalysts. Thus, it is required a method for not depositing or adhering the active component to the lateral face.
In this method, a slurry containing the active component is raised from the bottom face of carrier into the cells, and after the slurry has reached the top face of the carrier, the slurry in the cells is discharged from the lower side in a state not overflowing the top face. For preventing the slurry from overflowing the top face, it may cite a visual observation. It may use a laser or supersonic sensor in consideration of productivity.
The method using such a sensor, however, has the problem of not satisfactorily corresponding to variations in the viscosity and the speed of forced penetration of the slurry because it is incapable of confirming the position of the slurry with accuracy till the slurry reaches the top face, and capable of detecting the liquid level only after the slurry has surpassed the top face. Thus, in order to coat the slurry to the carrier completely, it has entailed the problem of suffering the slurry to overflow the top face and come to adhere to the lateral face and the device being used for the deposition.
We have pursued a diligent study of a method capable of accurately detecting the liquid level of the slurry at the proximity of the top face of the carrier while the slurry is ascending in the interior of the carrier, and have found that the position of liquid level of the slurry can be accurately detected by a water-detecting sensor. This invention has been perfected as a result.
The object of this invention is accomplished by a method for the production of a catalyst, characterized by adopting a water-detecting sensor for detecting the liquid level at the top face of a monolithic carrier while a liquid substance containing a catalytic component to be deposited is being introduced into the carrier from the bottom face.
According to the present invention, it can eliminate the problems of the conventional method such as the adhesion of the liquid substance overflowing the top face of the carrier to the lateral face and the device being used for the deposition and the consequent loss of the expensive liquid substance and spotting of the carrier and device used. It also permits a saving in the cost of production by ensuring safety of coating and decreasing the loss of liquid substances.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.